1. Field of the Invention
The present invention relates to a magnetic head with an underlying, longitudinal multilayer magnetoresistor. It is used in magnetic recording. The head according to the invention can be a read-only head and form a sensor, or can be a read-write head.
2. Discussion of Background
The invention essentially applies to horizontal, thin film heads. Such a head is shown in FIG. 1. It is possible to see therein in section a semiconductor substrate 10, a lower pole piece 12 with a conductor winding 13, which is generally in double spiral form. An insulating ridge 14 is located on the upper portion of the head and has a flat apex and two inclined sides. It is surmounted by an upper magnetic layer 16. This layer adopts the shape of the ridge and consequently has two horizontal, lateral portions 18.sub.1, 18.sub.2, two inclined, intermediate portions 20.sub.1 and 20.sub.2 corresponding to the sides of the ridge and two horizontal, central portions 22.sub.1, 22.sub.2 covering the apex of the ridge and forming the pole pieces of the head. These pole pieces are separated by a head gap 24.
The head also has a magnetoresistant element MR passing from one end 18.sub.1 to the other 18.sub.2 of the upper magnetic layer 16. This element is in contact with the magnetic layer 16 and forms a closed magnetic circuit therewith.
A conductor element 30 traversed by a current in a direction perpendicular to the plane of the drawing serves as the polarization means.
The magnetic writing circuit formed by the upper layer 16 and the lower layer 12 is interrupted by two auxiliary gaps 26.sub.1, 26.sub.2 formed between the two magnetic layers 12, 16. In other variants, these auxiliary gaps are located elsewhere and there may only be one such gap. The aim of these gaps is to increase the reluctance of the writing circuit and favour the reading circuit comprising the magnetoresistor. Such a head is described in EP-A-475 397.
Although satisfactory in certain respects, this type of head has a disadvantage associated with the weakness of the measuring signal. The magnetic reading flux is subdivided between a first circuit constituted by the upper magnetic layer 16 and the magnetoresistor MR and a second circuit constituted by the upper magnetic layer and the lower magnetic layer, so that the flux proportion traversing the magnetoresistor remains low, despite the interruption of the second magnetic circuit.
The object of the present invention is to obviate this disadvantage.